Which of the following is a herbicide?

$A$ molecule $M$ associates in a given solvent according to the equation $nM \rightleftharpoons (M)_n$. For a certain concentration of $M$,the van't Hoff factor was found to be $0.9$ and the fraction of associated molecules was $0.2$. The value of $n$ is:

Newton's law of cooling is a special case of

Which one of the following is not used for the construction of ecological pyramids?

The distance between two coherent sources is $0.1 \, mm$. The fringe-width on a screen $1.2 \, m$ away from the source is $6.0 \, mm$. The wavelength of light used is $\dots \, \mathring{A}$.

If the line $3x - 2y + 6 = 0$ meets the $X$-axis and $Y$-axis at points $A$ and $B$ respectively,then the equation of the circle with radius $AB$ and center at $A$ is: